Cavitation is the term used to describe the formation of gas cavities within a liquid. In a hydraulic system, this is normally taken to mean formation of vapor bubbles within the oil. But it can also mean dissolved air coming out of solution in the oil.
Cavitation erosion occurs when gas cavities in the oil collapse (implode) under pressure, in proximity to a metal surface. But in a hydraulic system, the formation of gas cavities is usually (but not always) associated with the presence of a vacuum (negative gauge pressure). And the presence of vacuum-induced, mechanical forces can be far more damaging, and catastrophically so, to hydraulic components, than pressure-induced bubble implosion.
How many different causes of cavitation in a hydraulic system can you come up with? Here are 20:
1. Clogged suction strainer (or just the presence of one!).
2. Wrong fluid viscosity.
3. Excessively low fluid temperature.
4. Excessively high fluid temperature.
5. Clogged reservoir breather.
6. Pump intake line too small in diameter.
7. Pump intake drop pipe inside tank inlet area too small.
8. Pump mounted too far above reservoir.
9. Pump mounted too far from the reservoir.
10. Excessive pump drive-shaft RPM.
11. Excessive pump swivel speed (variable displacement units).
12. Too many bends in pump intake line.
13. Turbulence caused by intake-line isolation valve, e.g. butterfly type.
14. Collapsed pump intake hose.
15. Other restriction in pump intake line.
16. Charge pump wear or failure (closed-circuit HST’s).
17. Excessive internal leakage (closed-circuit HST’s).
18. Faulty or incorrectly adjusted anti-cavitation or load-control valves.
19. Excessive pressure gradient–decay in working pressure too rapid.
20. Open return condition.
Whatever the cause, cavitation is detrimental to the long-run reliability of any hydraulic system. Which means tolerating its occurrence is a costly mistake. And to discover six other costly mistakes you want to be sure to avoid with your hydraulic equipment, get “Six Costly Mistakes Most Hydraulics Users Make… And How You Can Avoid Them!” available for FREE download here.